Andrew J. Wilkinson et al disclose luminescent complexes, in an article entitled, “Luminescent Complexes of Iridium (III) Containing N^C^N-Coordinating Terdentate Ligands,” published in Inorganic Chemistry vol. 45, no. 21, 2006, p8685-8699. The luminescent complexes include two bis-tridentate iridium complexes (i.e., complexes 3 and 4 shown in Scheme 5 of the article). As disclosed on page 8690, from line 30 of the left column to line 3 of the right column, the yields of the complexes 3 and 4 are 37% and 21%, respectively, which are relatively low. Thus, the complexes 3 and 4 are not suitable for use as a material for making organic light-emitting diodes (OLEDs).